(a) Field of the Invention
The present invention relates to a modular, self-supporting flight of stairs comprising at least two pairs of stringer units each acting as a support for a thread-step. The invention also relates to the stringer units used for the fabrication of this flight of stairs.
(b) Description of the Prior Art
Numerous modular, self-supporting flights of stairs of different structure are already known and commercially available in the market for arranging in a very fast manner, any king of building space comprising floors at different levels. Examples of such already known flights of stairs are disclosed and claimed in U.S. Pat. Nos. 2,593,683 of 1952; 2,724,466 of 1955; 2,760,239 of 1956 and 3,196,397 of 1965 and Canadian Pat. No. 600,821 of 1960.
If the flights of stairs disclosed in these patents all have the advantages of being of a relatively simple structure and therefore installable in a very fast manner even by a not specialized labor, however they all have also the drawback of being not very stable against lateral pressure because of the relative thinness of their stringers even when these stringers are provided with reinforcing flanges, and not very resistant with respect to the load they can support because each of their stringers is fixed to the stringer immediately inferior or superior thereto by means of bolts or rivets that are subject in use to very substantial shearing forces.
Thus, one can see that the bolts used for fixing the modular stringers of the flight of stairs disclosed in U.S. Pat. No. 2,593,683 are permanently subject to vertical shearing forces while the bolts used for fixing the modular stringers of the flight of stairs disclosed in U.S. Pat. Nos. 2,724,466 and 3,196,997 are also subject to shearing forces that are applied to the bolts in an inclined plane corresponding to the plane of the stairs. In a similar manner, the screws used for fixing the modular steps of the flight of stairs disclosed in U.S. Pat. No. 2,760,239 to their supporting, wood stringers are subject to vertical shearing forces as are the nails used for fixing the steps of the stairs disclosed in Canadian Pat. No. 600,821 to their wood stringers.